Recently, as electronic apparatuses such as portable telephones, PDPs, and personal computers have been demanded to have high performance and small size, electronic components such as semiconductor elements have had high performance and high density. Consequently, the amount of heat generation of electronic components is remarkably increased, and therefore it is important to suppress the increase in temperature of electronic apparatuses.
In order to suppress the increase in temperature of electronic apparatuses, a thermal connection structure shown in FIG. 8 is used. The thermal connection structure includes semiconductor package 41 incorporating a semiconductor element as a heat generator; heat sink 42 as a heat radiator; and thermal connection portion 43 for thermally connecting the heat generator and the heat radiator (see, for example, Patent Document 1).
Semiconductor package 41 is electrically connected to a conductor circuit of printed wiring board 46 via a terminal. Heat sink 42 is made of a metal such as an aluminum alloy and composed of a plate-shaped core and a plurality of plate-fins disposed upright on the core.
Thermal connection portion 43 is provided between semiconductor package 41 and heat sink 42 to improve the heat radiation performance from semiconductor package 41 to heat sink 42. Thermal connection portion 43 is brought into contact with semiconductor package 41 and heat sink 42 by tightening and pressurizing with the use of attaching components 45 such as screws.
Thermal connection portion 43 is formed of a heat radiation sheet having an excellent thermal conductivity to enhance a cooling effect. Examples of the known heat radiation sheet of this kind include pyrolytic graphite sheet 44 which is formed by firing a polymer film such as a polyimide film at high temperatures and which has a high thermal conductivity. Since pyrolytic graphite sheet 44 has flexibility, when it is pressurized in the thermal connection structure, the surface of pyrolytic graphite sheet 44 can be brought into close contact with the surfaces of semiconductor package 41 and heat sink 42.
Furthermore, a heat radiating member of fluid resin such as silicone grease and silicone oil is applied to the surface of pyrolytic graphite sheet 44. Thus, the heat radiating member enters the concavity and convexity on the surfaces of semiconductor package 41, heat sink 42 and pyrolytic graphite sheet 44 so as to reduce air space in gaps, thereby enhancing the adhesion and reducing the contact thermal resistance of thermal connection portion 43.
In particular, in order to enhance the thermal conductivity of a fluid heat radiating member, a fluid heat radiating member containing a thermal conductive filler such as high thermal conductive aluminum nitride is used. In such a case, however, since the concavity and convexity on the surface of pyrolytic graphite sheet 44 are formed in firing a polymer, gaps are not large enough to contain thermal conductive fillers. Therefore, almost all of the thermal conductive fillers move on the surface of pyrolytic graphite sheet 44 and are pushed out to the outer periphery when thermal connection portion 43 is pressurized. As a result, a thermal resistance of thermal connection portion 43 cannot be reduced.